1. Field of the Invention
The present invention relates to an electric oven, and more particularly, to an electric oven which increases temperature fast and reduces heat loss in accordance with that a cavity surface generates its own heat by using an induction heating.
2. Description of the Related Art
Generally, an electric oven is a cook used in the kitchen having its own heating means. The electric oven usually cooks food in a cooking chamber by using heat of an electric heater as a heating source, but sometimes uses microwave as a subsidiary heating source by mounting a magnetron.
FIG. 1 is a schematic perspective view showing a construction of an electric oven in accordance with the conventional art, in which a heater is mounted as a main heating source, and microwave is used as another heating source.
As shown, the conventional electric oven has a case 100 composed of a plurality of plates, which constitutes an appearance. For example, the electric oven can be composed of a plate for forming a lower surface thereof and cabinets for forming both sides and an upper surface thereof.
A cavity 200 into which food is put and cooking is performed is formed in the case 100.
The cavity 200 is selectively opened and closed by a door 130. A lower end of the door 130 is hinge-coupled to a front surface of the cavity 200, and a door handle 132 is formed at an upper end of the door 130. Accordingly, when the door handle 132 is pulled, the upper end is rotated downwardly on the basis of the lower end, thereby opening and closing the cavity 200. A managing unit 160 is provided at an upper end of the electric oven which is not shielded by the door 130. Generally, each kind of button required to manage the electric oven, and a display window for displaying an operation state of the electric oven can be formed at the managing unit 160.
A lower heater 112 is installed at a lower side of the cavity 200. The lower heater 112 generally uses a sheath heater. The lower heater 112 transmits heat to the cavity 200 through an inner bottom of the cavity 200.
An upper heater 110 is installed at an upper side of the cavity 200, which also uses the sheath heater, generally.
The sheath heater is composed of a metal pipe at an outer portion, a heat line located in the metal pipe, and an insulating material installed between the metal pipe and the heat line. The sheath heater is well know, thereby omitting its detail explanation.
In the meantime, a convection heater 114 is installed at a back side of the cavity 200. Also, a convection fan 140 is installed at the rear side of the cavity 200 where the convection heater 114 is installed. The convection fan 140 supplies air heated by the convection heater 114 to the cavity 200. To this end, a plurality of through holes 142 are formed at the back side of the cavity 200 corresponding to the convection heater 114.
A magnetron 150 for supplying heat to the cavity 200 as another heating source is formed at a space between an upper portion of the cavity 200 and the case 100. The magnetron 150 oscillates microwave and supplies heat to the cavity 200. The magnetron 150 supplies the microwave into a wave guide 152 mounted at the upper surface of the cavity 200. A reference numeral 144 denotes a cooling fan for cooling components including the magnetron 150. Other components for supplying the microwave will not be explained.
A reference numeral 180 denotes an oven lamp for lightening inside of a cooking chamber.
Operations of the conventional electric oven will be explained as follows.
Food is put on the cavity 200, the door 130 is closed, and a power source is supplied in a state that the cooking chamber is shielded from outside, thereby performing cooking. That is, when the power source is supplied, heat from the lower heater 112 is conducted to the bottom of the cavity 200. The conducted heat heats air in the cavity 200, and the heated air is transmitted to the food. Also, the upper heater 110 transmits heat to the food by radiation and convection, and the heat supplied from the convection heater 114 is transmitted to the cooking chamber as hot blast through the plurality of holes 142 by the convection fan 140 and transmitted to the food.
Meantime, the microwave oscillated from the magnetron 150 can be used to cook the food by the user's selection.
Hereinafter, problems of the conventional electric oven will be also explained.
The electric oven has to be heated in advance as a predetermined temperature before cooking. Also, in order to use an automatic cleaning function using pyrolysis in the cavity 200, an inner temperature of the electric oven has to be increased more than 500° C. and then considerable time has to lapse to combust oil of an inner wall.
The lower heater 112 and the upper heater 110 use the sheath heater. However, the sheath heater takes much time in increasing temperature up to a saturation temperature since specific heat is great. Also, since the lower heater 112 is not completely in contact with the lower surface of the cavity 200, contact heat resistance is great. Besides, heat efficiency is degraded by depending on natural convection having a low transmittance efficiency and the radiation which requires great temperature difference with the lower surface of the lower heater 112.
Also, another heat source does not exist at both sides of the cavity 200. Accordingly, said both sides of the cavity 200 are heated by heat conducted through the plates constituting the cavity 200 or heat transmitted by air flow in the cooking chamber. Eventually, since temperature of said both sides of the cavity 200 can be increased into a predetermined value after temperature of other parts is increased, much preheating time is required.
Accordingly, when cooking is to be performed or an outer surface of the cavity is to be cleaned, temperature of said both sides of the cavity 200 has to be increased more than temperature which is required for pyrolysis of other parts. As a result, consumption power is increased and a heatproof design becomes difficult.